Abstract

In this research work, in-tube condensation in the presence of air is investigated experimentally for different operating conditions, and inhibiting effect of air is analyzed by comparing the experimental data of air/steam mixture with the data of corresponding pure steam cases, with respect to temperature, heat flux, air mass fraction, and film Reynolds number. The test matrix covers the range of; Pn=2–6 bars, Rev=45,000–94,000, and Xi=0 % – 52 %. The inhibiting effect of air manifests itself as a remarkable decrease in centerline temperature (10 °C – 50 °C), depending on inlet air mass fraction. However, the measured centerline temperature is suppressed compared to the predicted one, from the Gibbs-Dalton law, which indicates that the centerline temperature measurements are highly affected by inner wall thermal conditions, possibly due to narrow channel and high vapor Reynolds number. Even at the lowest air quality (10 %) the reduction of the local heat flux is 20 % while it reaches up to 50 % for the quality of 40 %. Vapor mass flow rate may dominate over system pressure, concerning the effect on local heat flux, for cases with air/vapor mixture. The situation is rather different in pure vapor runs, that is increase in system pressure has a strong effect on enhancement of predicted, and even measured, wall subcooling degree and hence on increase in local heat flux. The investigation for the effect of superheating of steam on condensation process reveals the fact that inlet superheating of steam has no considerable effect on heat flux. The calculated film Reynolds number decreases as air mass fraction increases at the same system pressure setting, and falls into the range of turbulent region (Ref > 300) for almost all experimental runs. The RELAP5 code overpredicted majority of experimental local heat flux data by 5 % – 50 %.